The present invention relates generally to air bags of the type utilized in vehicle occupant restraint systems. More particularly, the present invention relates to fabric suitable for use in such air bags.
For some time, vehicle manufacturers have been equipping their products with air bag systems to supplement the protection offered by seatbelts. These air bag systems utilize at least one folded air bag in fluid communication with a source of inflation gas. When a collision is detected between the vehicle and another object, the source of inflation gas is actuated to inflate the air bag.
Air bags have traditionally been of two types, i.e., driver side and passenger side. More recently, some vehicle manufacturers have also begun providing air bags designed for side-impact protection. Air bags of a particular type will be constructed to satisfy unique operating characteristics of that type. For example, driver side air bags have frequently been made from coated fabric or uncoated fabric of very low permeability. Passenger side air bags have often been made from uncoated fabric of slightly higher permeability.
Several primary fabrics have been utilized in the production of vehicle air bags. An early fabric widely employed for driver side air bags was woven from 840 denier yarn into a thread count of approximately 25.times.25 and coated with 1-2 ounces per square yard of neoprene rubber. As demand increased for reduced packaging in driver side applications, the industry moved toward smaller denier yarns of a higher thread count. For example, fabrics woven from 420 denier yarn into thread counts of approximately 49.times.49 or 46.times.46 were utilized.
As intended, these 420 denier fabrics successfully provided the reduced packaging sought by vehicle manufacturers. Because the denier and tensile strength of the yarn had been reduced, however, the yarn had to be slashed with a suitable sizing compound, such as polyacrylic acid (PAA), prior to rapier weaving. The greige cloth, stiff and boardy due to the sizing compound, then had to be scoured prior to use. Scouring was also necessary to remove residual spin finish which, along with the size, had a tendency to prevent good adhesion of the neoprene coating compound. With the additional processing of slashing and full scouring, the cost of the fabric was increased.
The additional cost of sizing and scouring was also seen in another important fabric. This fabric, which has been used primarily in passenger side applications, was woven into a 32.times.32 ripstop configuration from 840 denier yarn. Size was used despite the stout nature of 840 denier yarn because the beat-up at the fell of the cloth was very tight, often causing chafing of unsized yarn during the weaving process.
Much of the world market has traditionally been processed using conventional rapier weaving technology because of its versatility and quality. Typical rapier goods were very dense in construction, like the 49.times.49 420 denier fabric discussed above, as well as 60.times.60 315 denier or 41.times.41 630 denier fabrics.
Recently, some fabric makers began using water jet weaving as an alternative method of producing air bag fabric. An advantage of water jet weaving is that some normal process steps can be eliminated or reduced. For example, improvements in the overall quality of the yarns themselves often allow water jet looms to be run without size on the warp yarns. The chilled water holds and protects the unsized warp yarns during cloth formation, whereas these yarns could be bruised and frayed when run dry on a rapier loom machine. The scouring process can be eliminated since size was not used and the spin finish on the yarns is partially broken down during the weaving process and is brought down to previous market levels of acceptability through normal heat setting of the fabric.
Although water jet weaving has certain advantages, it also has various drawbacks. One significant drawback for air bag fabric is a relatively wide variation in air permeability across the fabric web. In particular, water jet weaving has a tendency to blossom the fabric, particularly at the edges. As such, the side-center-side permeability of the fabric will generally not be as consistent as rapier goods.
In addition, greige cloth produced on a water jet loom must be dried to prevent growth of mildew. In addition, water jet looms have traditionally required a more difficult changeover process when it is desired to weave a different type of fabric on a particular loom. Water jet looms also tend to be less flexible with respect to on-loom constructions and the quality of the fabric can be inconsistent.